Re: [RFC PATCH v6 1/5] Thread-local ABI system call: cache CPU number of running thread

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Florian Weimer <fweimer@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Russell King <linux@arm.linux.org.uk>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-api <linux-api@vger.kernel.org>,
	Paul Turner <pjt@google.com>, Andrew Hunter <ahh@google.com>,
	Andy Lutomirski <luto@amacapital.net>,
	Andi Kleen <andi@firstfloor.org>,
	Dave Watson <davejwatson@fb.com>, Chris Lameter <cl@linux.com>,
	Ben Maurer <bmaurer@fb.com>, rostedt <rostedt@goodmis.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Josh Triplett <josh@joshtriplett.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Michael Kerrisk <mtk.manpages@gmail.com>,
	Boqun Feng <boqun.feng@gmail.com>
Subject: Re: [RFC PATCH v6 1/5] Thread-local ABI system call: cache CPU number of running thread
Date: Thu, 7 Apr 2016 09:59:36 -0700	[thread overview]
Message-ID: <CA+55aFyB98SrhVPL66DAb3+rbn7nHf6K2MmEQD2Uj7F6hNcQEQ@mail.gmail.com> (raw)
In-Reply-To: <57068FCC.8000701@redhat.com>

On Thu, Apr 7, 2016 at 9:50 AM, Florian Weimer <fweimer@redhat.com> wrote:
>
> (AFAICS set_robust_list was designed with such extensions in mind.)

This is a disease among people who have been taught computer science.
People think that "designing with extensions in mind" is a good idea.

It's a _horrible_ idea.

If you think that "design with extensions in mind" is a good idea,
you're basically saying "I don't know what I might want to do".

I'm not interested in those kinds of kernel interfaces. EVERY SINGLE
TIME when we add a new random non-standard interface that isn't
already used by lots and lots of people, the end result is the same:
nobody actually uses it. There might be one or two very obscure
libraries that use it, and then a couple of special applications that
use those libraries. And that's it.

So unless there is a clear use-case, and clear semantics that people
can agree on as being truly generic and useful for a lot of different
cases, excuse me for being less than impressed.

Anything with a "let's add feature fields" is broken shit. BY DEFINITION.

See my argument?

And btw, ask yourself how well that set_robust_list() extension worked?

(Answer sheet to the above question: it was pure garbage. Instead of
actually ever being extended, the "struct robust_list_head" not only
is fixed, it was horribly misdesigned to the point of requiring a
compat system call. Pure garbage, in other words, and an example of
how *not* to do user interfaces).

                 Linus